Alkylene oxides, for example ethylene oxide, propylene oxide and butylene oxide, have been subjected to liquid phase hydration to produce the corresponding alkylene glycols. Commercially, in the production of ethylene glycol from ethylene oxide large molar excesses of water are used (See: Kirk-Othmer: Encyclopedia of Chemical Technology Volume 11, Third Edition, Page 939, (1980)). It has been reported that the presence of large quantities of water in the reaction system are necessary if the yield to the desired monoalkylene glycol is to be great enough to be commercially viable and minimize the production of by products such as diglycols and triglycols. Accordingly, the commercial practice has generally involved the hydration of an alkylene oxide at a temperature of about 100.degree. C. to about 200.degree. C. in the presence of a large molar excess of water, for example, in excess of 15 moles of water per mole of alkylene oxide, when the corresponding monoalkylene glycol is to be produced. Unfortunately, the use of such large excesses of water presents significant energy and equipment requirements for its removal.
Since the selectivity of the hydration process to monoglycol, e.g., ethylene glycol, propylene glycol or butylene glycol, is dependent on the by products formed, it would be desirable to provide a process that would increase the selectivity of the hydration process to monoglycol products. In addition, any process which would favorably decrease the relative amount of water employed to alkylene oxide hydrated while not increasing, or preferably decreasing, the by products formed would be advantageous. Thus, the energy and equipment requirements would necessarily be less for separation and purification processes relating to the removal and recovery of the monoglycol from water and by products.
As a result of the desire to improve the hydration process, both in terms of selectivity to desired product and the energy requirements to effect the purification and recovery of the desired product, several processes have been suggested which provide for the hydration of an alkylene oxide in the presence of a specific catalyst such that the ratio of water to alkylene oxide may be lowered and such that the selectivity to monoglycol product is maintained or enhanced.
Numerous catalysts have been suggested for use in the hydration of alkylene oxides, including the use of acid catalysts such as: alkyl sulfonic acid ion exchange resins (U.S. Pat. No. 4,165,440); carboxylic acids and halogen acids (U.S. Pat. No. 4,112,054); strong acid cation exchange resins (U.S. Pat. No. 4,107,221); aliphatic monocarboxylic and/or polycarboxylic acids (U.S. Pat. No. 3,933,923); cationic exchange resins (U.S. Pat. No. 3,062,889); acidic zeolites (U.S. Pat. No. 3,028,434); sulfur dioxide (U.S. Pat. No. 2,807,651); Ca.sub.3 (PO.sub.4).sub.2 (U S. Pat. No. 2,770,656); high melting polyvalent metal fluorides (U.S. Pat. No. 2,547,766); trihalogen acetic acid (U.S. Pat. No. 2,472,417); and copper-promoted aluminum phosphate (U.S. Pat. No. 4,014,945).
In addition to the acid catalysts, numerous catalysts have been suggested for the hydration of alkylene oxides in the presence of carbon dioxide. These include alkali metal halides, such as chlorides, bromides and iodides, quaternary ammonium halides such as tetramethyl ammonium iodide and tetramethyl ammonium bromide (British Pat. No. 1,177,877); organic tertiary amines such as triethylamine and pyridine (German published patent application No. 2,615,595, Oct. 14, 1976, and U.S. Pat. No. 4,307,256, issued Dec. 22, 1981); quaternary phosphonium salts (U.S. Pat. No. 4,160,116, issued July 3, 1979); and chlorine or iodine type anion exchange resins (Japanese Kokai No. 57/139,026, published Aug. 27, 1982); and partially amine neutralized sulfonic acid catalyst, e.g., partially amine neutralized sulfonic acid resin (U.S. Pat. No. 4,393,254, issued July 12, 1983).
Although a review of the results reported in the patent literature would suggest that the above described catalysts have provided commercially acceptable results, that is, a high selectivity to the monoglycol product and a decrease in the requirement for large molar excess of water, these catalysts have not been commercially employed for several reasons. For example, alkali metal halides tend to corrode the reaction system at the temperatures employed for the hydration of alkylene oxides. The relatively low solubility of alkali metal halides and quaternary ammonium halides in alkylene glycol restricts their use as hydration catalysts since they are likely to precipitate within the reaction system during the course of the hydration reaction and can result in problems associated with cleaning the reaction system. In addition, some catalysts, such as tertiary amines, have certain chemical and physical properties which prevent their ready use as hydration catalysts. For example, tertiary amines have a strong pungent odor which is not desirable in manufacturing and can detract from the quality of the end product.
U.S. Pat. No. 4,277,632, issued July 7, 1981, discloses a process for the production of alkylene glycols by the hydrolysis of alkylene oxides in the presence of a catalyst of at least one member selected from the group consisting of molybdenum and tungsten. The patent discloses that the catalyst may be metallic molybdenum or metallic tungsten, or inorganic or organic compounds thereof, such as oxides, acids, halides, phosphorous compounds, polyacids, alkali metal and alkaline earth metal, ammonium salts and heavy metal salts of acids and polyacids, and organic acid salts. An objective of the disclosed process is stated to be the hydrolysis of alkylene oxides wherein water is present in about one to five times the stoichiometric value without forming appreciable amounts of by-products such as the polyglycols. The reaction may be carried out in the presence of carbon dioxide; however, when the reaction is carried out in the presence of nitrogen, air, etc., the patentees state that the pH of the reaction mixture should be adjusted to a value in the range of 5 to 10. Japanese Kokai No. JA 54/128,507, published Oct. 5, 1979, discloses a process for the production of alkylene glycols from alkylene oxides and water using metallic tungsten and/or tungsten compounds.
Japanese Kokai No. JA 56/073,035, published June 17, 1981, discloses a process for the hydrolysis of alkylene oxide under a carbon dioxide atmosphere in the presence of a catalyst consisting of a compound containing at least one element selected from the group of titanium, zirconium, vanadium, niobium, tantalum and chromium. The compounds include the oxides, sulfides, acids, halides, phosphorous compounds, polyacids, alkali metal salts of acids and polyacids, ammonium salts of acids and polyacids, and heavy metal salts of acids.
Japanese Kokai No. JA 56/073,036, published June 17, 1981, discloses a process for the hydrolysis of alkylene oxide under a carbon dioxide atmosphere in the presence of a catalyst consisting of a compound containing at least one element selected from a group comprising aluminum, silicon, germanium, tin, lead, iron, cobalt and nickel.
Japanese Kokai No. JA 56/92228, published July 25, 1981, is directed to processes for producing highly pure alkylene glycols. The disclosure is directed to a distillation procedure for recovery of a molybdenum and/or tungsten containing catalyst from an alkylene oxide hydrolysis process in the presence of carbon dioxide. The application states that the catalyst is at least one compound selected from the group consisting of compounds of molybdenum and tungsten which compound may be in combination with at least one additive selected from the group consisting of compounds of alkali metals, compounds of alkaline earth metals, quaternary ammonium salts and quaternary phosphonium salts. The preferred catalysts are stated to be molybdic acid, sodium molybdate, potassium molybdate, tungstic acid, sodium tungstate and potassium tungstate. Potassium iodide is the only additive employed in the examples.
Patent applications Ser. Nos. 428,815, filed Sept. 30, 1982, (now abandoned) and 530,235, filed Sept. 8, 1983, of J. H. Robson and G. E. Keller, disclose the production of monoalkylene glycols with high selectivity by the reaction of a vicinal alkylene oxide with water in the presence of a water-soluble metavanadate. Hence, lower water to alkylene oxide ratios can be employed using the disclosed process with attractive selectivities to the monoglycol products. The counter ion to the metavanadate is selected to provide a water-soluble metavanadate salt under the reaction conditions employed and alkali metals, alkaline earth metals, quaternary ammonium, ammonium, copper, zinc, and iron are suggested cations. It is also disclosed that the metavanadate may be introduced into the reaction system in the salt form or on a support such as silica, alumina, zeolites and clay. Since the metavanadate ion is water-soluble, it can be lost from the reaction system and means must be provided to recover it from the effluent from the reaction zone.
Unfortunately, insoluble salts of vanadate anion, such as calcium vanadate, as well as insoluble molybdate and other metalate salts do not appear to provide the selectivity toward the monoglycol products which is achievable with the water-soluble metalates. The problems with the recovery of the metalate are significant factors in considering the use of the technology on a commercial scale.
Japanese Kokai No. JA 57/139,026, published Aug. 27, 1982, discloses a process for the hydrolysis of alkylene oxides in the presence of carbon dioxide and a halogen type anion exchange resin as a catalyst. The exemplified catalyst is a chlorine type anion exchange resin (Dowex MSA-1(TM), a product of the Dow Chemical Company) and a similar iodine-type anion exchange resin. At a mole ratio of alkylene oxide to water of about 0.66, the selectivity to monoethylene glycol was reported to be 91.0 percent using the chlorine type anion exchange resin and 89.6 percent using the iodine-type anion exchange resin. In the absence of carbon dioxide, the application disclosed that a selectivity to the monoethylene glycol of 34.8 percent was obtained and an unpleasant smell was noted in the product. In the absence of any anion exchange resin and in the presence of carbon dioxide, the selectivity to monoethylene glycol was reported to be 37.5 percent. All of the examples were conducted in an autoclave immersed in an oil bath at a temperature of 150.degree. C. The disclosure reports that the maximum reaction liquid temperature was 130.degree. C. and the reaction was carried out for 90 minutes. While the application did not specifically indicate the source of the unpleasant smell which originated in the comparative example where the carbon dioxide atmosphere was not employed, it could have been the result of degradation of the anion exchange resin.
Copending U.S. Patent application Ser. No. 594,385 of J. R. Briggs and J. H. Robson, is directed to processes for the hydrolysis of alkylene oxide with enhanced selectivities to monoalkylene glycols using a reaction menstruum comprising an agueous phase, a water-immiscible liquid phase and a metalate anion-containing material wherein the concentration of the metalate anion-containing material in the water-immiscible phase is greater than that in the aqueous phase.